Various methods of filtration, wellbore isolation, production control, wellbore lifecycle management, and wellbore construction are known in the art. The use of shaped memory materials in these applications have been disclosed for oil and gas exploitation. Shape-memory materials are smart materials that have the ability to return from a deformed state (temporary shape) to their original (permanent) shape induced by an external stimulus or trigger (e.g. temperature change). In addition to temperature change, the shape memory effect of these materials may also be triggered by an electric or magnetic field, light or a change in pH. Shape-memory polymers (SMPs) cover a wide property range from stable to biodegradable, from soft to hard, and from elastic to rigid, depending on the structural units that constitute the SMP. SMPs include thermoplastic and thermoset (covalently cross-linked) polymeric materials. SMPs are known to be able to store multiple shapes in memory.
Dynamic Mechanical Analysis (DMA), dynamic mechanical thermal analysis (DMTA) or dynamic thermomechanical analysis is a technique used to study and characterize SMP materials. It is most useful for observing the viscoelastic nature of these polymers. The sample deforms under a load. From this, the stiffness of the sample may be determined, and the sample modulus may be calculated. By measuring the time lag in the displacement compared to the applied force it is possible to determine the damping properties of the material. The time lag is reported as a phase lag, which is an angle. The damping is called tan delta, as it is reported as the tangent of the phase lag.
Viscoelastic materials such as shape-memory polymers typically exist in two distinct states. They exhibit the properties of a glass (high modulus) and those of a rubber (low modulus). By scanning the temperature during a DMA experiment this change of state, the transition from the glass state to the rubber state, may be characterized. It should be noted again that shaped memory may be altered by an external stimulus other than temperature change.
The storage modulus ε′ (elastic response) and loss modulus ε″ (viscous response) of a polymer as a function of temperature are shown in FIG. 1. The nature of the transition state of the shaped memory polymer affects material's shape recovery behavior and can be descriptive of the polymer's shape recovery. Referring to FIG. 1, the Glass State is depicted as a change in storage modulus in response to change in temperature which yields a line of constant slope. The Transition State begins when a slope change occurs in the storage modulus as the temperature is increased. This is referred to as the Tg Onset which in FIG. 1 is approximately 90° C. The Tg Onset is also the point where shape recovery can begin. Tg for a shape-memory polymer described by FIG. 1 is defined as the peak of the loss modulus, which in FIG. 1 is approximately 110° C. If the slope's change of the storage modulus were represented by a vertical line of undefined slope, the material shape recovery would occur at a specific temperature and transition immediately from the glassy state to the rubber state. Generally, the more gradual the slope change of the storage modulus in the transition state, the greater the range of temperatures which exhibit characteristics of both the glass and rubber states. The transition state is the area of interest for the SMP material's shape recovery characteristics. It should also be evident that shape recovery would occur more slowly if stimulus temperature is closer the Tg Onset temperature and shape recovery would be more rapid as the stimulus temperature approached or exceeded the Tg.
One method of making use of the unique behavior of shape-memory polymers is via temperature response described above. An example is seen in FIG. 2. The finished molded part 100 of shape-memory polymer has a defined Tg and Tg Onset. This may be considered an original geometric position of the shape-memory material. The part is then heated close to the Tg of the polymer. Force is applied to the finished part to reshape the part into a different configuration or shape 100′. This may be considered an altered geometric position of the shape-memory material. The reshaped part 100′ is then cooled below the shape-memory polymer's Tg Onset and the force removed. The finished part 100′ will now retain the new shape until the temperature of the part is raised to the Tg Onset at which point shape recovery will begin and the part will attempt to return to its original shape 100″ or if constrained, the part will conform to the new constrained shape 100′. This shape 100″ may be considered the shape-memory material's recovered geometric position.
U.S. Pat. No. 7,318,481 assigned to Baker Hughes Incorporated disclosed a self-conforming expandable screen which comprises a thermosetting open cell shape-memory polymeric foam. The foam material composition is formulated to achieve the desired transition temperature slightly below the anticipated downhole temperature at the depth at which the assembly will be used. This causes the conforming foam to expand at the temperature found at the desired depth.
It would thus be very desirable and important to discover a method and device for deploying an element made of shaped memory materials at a particular location downhole to achieve some desired element of filtration, wellbore isolation, production control, wellbore lifecycle management, and wellbore construction. Generally, the more versatility for deploying an element the better, as this gives more flexibility in device designs and provides the operator more flexibility in designing, placement and configuration of the wellbore devices.